The invention relates to a fault current limiter, with a superconducting device comprising a sequence of superconducting elements, each with an electrically conducting substrate, a superconducting film, and an electrically insulating intermediate layer provided between the substrate and the superconducting film, wherein the superconducting films of adjacent superconducting elements of the sequence are electrically connected, in particular in series, wherein the electrically conducting substrate of each superconducting element of the sequence is electrically insulated from each electrically conducting substrate of those adjacent superconducting elements within the sequence whose superconducting films are electrically connected in series with the superconducting film of said superconducting element, wherein the superconducting films of at least some adjacent superconducting elements are electrically connected by means of a bridge element, wherein the bridge element comprises a superconducting section and wherein the superconducting films of the adjacent superconducting elements electrically connected by means of bridge element are both electrically connected to the superconducting section, and wherein the bridge element overlaps. In particular partially overlaps, with both adjacent superconducting elements electrically connected by means of the bridge element.
Such a superconducting device is known from U.S. Pat. No. 5,986,536.
Superconducting fault current limiters are used to limit the current flow through the load side of an electric circuitry in case of a short circuit on the load side. In the most simple case, the fault current limiter comprises a superconducting device connected in series with the load. The superconducting device can carry a current with very low loss. As long as the current through the superconducting device does not exceed the critical current, the superconducting device is practically invisible within the electric circuitry, and it is the characteristics, in particular the resistance, of the load which determine the current within the electric circuitry.
In case the resistance of the load drops (i.e. there is a short circuit within the load), the current in the circuitry increases, and eventually exceeds the critical current. In this case, the superconducting device quenches (i.e. becomes normally conductive) which results in a high ohmic resistance of the superconducting device. As a result, the current in the electric circuitry drops accordingly, and the load is protected from high electric current.
The superconductor material of a superconducting device must be cooled to a low temperature in order to attain its superconducting state. In order to facilitate and lessen the costs for the cooling, high temperature superconductor materials (HTS materials) may be used. HTS materials have a critical temperature above a temperature of 30 K, and can often be cooled with liquid nitrogen (LN2).
A fault current limiter with a superconducting device using a HTS material is known from U.S. Pat. No. 5,986,536. It comprises several superconducting elements, each comprising a HTS film deposited on an electrically insulating (dielectric) substrate, in particular made of a material that permits textured growth of the HTS film such as yttrium-stabilized ZrO2, with a thin interlayer of Ag. The superconducting elements, i.e. their HTS films, are connected in series.
Fault current limiters of this type comprising superconducting elements with textured superconducting films deposited on a dielectric substrate, are rather expensive to produce. Further, such fault current limiters have a relatively long recovery time after a quench event.
It is the object of the invention to introduce a fault current limiter which is cost efficient in production, and which is capable of a short recovery time after a quench event.